Long-term Weight Changes and Risk of Rheumatoid Arthritis Among Women in a Prospective Cohort: A Marginal Structural Model Approach.

OBJECTIVE To examine the association of long-term weight change with rheumatoid arthritis (RA) risk in a large prospective cohort study. METHODS The Nurses' Health Study (NHS) II started in 1989 (baseline); after exclusions, we studied 108,505 women 25-42 years old without RA. Incident RA was reported by participant and confirmed by medical record review. Body weight was reported biennially through 2015. We investigated two time-varying exposures: weight changes from baseline and from age 18; change was divided into 5 categories. We used a marginal structural model (MSM) approach to account for time-varying weight change and covariates. RESULTS Over 2,583,266 person-years, with a median follow-up time of 25.3 years, 541 women developed RA. Compared to women with stable weight from baseline, weight change was significantly associated with increased RA risk [weight gain 2- 2 kg: RR = 2.05 (95% CI 1.28, 3.28)]. Weight gain of 10 kg or more from age 18 compared with stable weight was also associated with increased RA risk [10-< 20 kg: RR = 2.12 (95% CI 1.37, 3.27), ≥20 kg: RR = 2.31 (95% CI 1.50, 3.56)]. Consistent findings were observed for seropositive and seronegative RA. CONCLUSION Long-term weight gain was strongly associated with increased RA risk in women, with weight gain of ≥ 20 kg associated with more than a three-fold increased RA risk. Maintenance of healthy weight may be a strategy to prevent or delay RA.